As it is widely known, liquid pipes used in waterworks and drainage works are laid underground. These liquid pipes can be damaged on a certain part due to deterioration and other causes, and it is not easy to grasp whether or not the pipes are damaged or the exact damaged part because they are laid underground.
For instance, in the case of the waterworks, up to 20% of tap water is leaking since the old waterworks pipes are not changed. However, the existing water leakage detecting system has a difficulty in detecting a small amount of leakage as well as knowing the exact leaking position. The existing method of detecting water leakage is as follows.
First, there is a method of detecting it by a geophone. In this case, a tool such as a sound detector is used or the hearing sense of a skilled expert is used. When the sound of leakage is transmitted to the surface of the earth, it is detected on the earth to amplify the sound. Therefore, it is available to listen to the sound by a receiver or detect the leakage by analyzing it with a meter.
However, since it depends on the sound detector or the hearing sense of a human being, it is possible to detect water leakage over the regular amount. Furthermore, the conduit of a waterworks pipe is supposed to be laid underground at less than 1.2 meters above the ground, making it difficult to detect water leakage when water leaks in a small quantity and to exactly detect the leaking area. In addition, in the case of the conduit of the waterworks pipes installed under the ground of the roads having heavy traffic instead of the exclusive sites, it is almost impossible to detect water leakage because traffic noise is transmitted as well.
Second, there is a method of detecting moisture leaking outside by a sensor when water leaks, by installing the moisture-detecting sensor outside of the pipes. A method of using a sound wave or the moisture-detecting sensor is done in a pipe attaching way, thereby immediately knowing water leakage through alarm signals. Thus, this method can be used for online monitoring. However, it is not easy to install the moisture-detecting sensor outside of the pipes since the soil contains water in itself.
Third, there is a method of separating the pipelines from the pipe networks by using the bypass line to inspect water leakage. With this method, the one end of the pipelines is closed after separating the pipelines, and an opening whose diameter is slightly bigger than the inside diameter of the pipe is pushed by water pressure. When it reaches the water leaking area, the opening is not pushed any more. That is, if the opening pushed by water pressure is not pushed any more, it means there is a leaking part on the spot.
But, when more than two separated leaking parts exist, it is difficult to detect the position of the middle leaking area or it is almost impossible to detect minute pipe cracks such as stress corrosion cracks, requiring a lot of time.
In the case of the drainage works, the soil can be polluted when water leaks. Unlike the waterworks, there are many artificial reasons for water leakage of the drainage works: wrong joining due to joining failure between the pipes; other pipe passing when the gas pipe passes through the drain pipes; joining part detachment due to the detached joining part between the pipes; and other foreign substance infiltration. To inspect these errors, it is common to use a method of searching the error-generated parts by CCTV, however it is necessary to dig the laid position over to inspect the errors with the existing methods, causing inconvenience of using inspection equipment.
In addition, a system of providing information on the status of each waterworks/drainage work forming the entire waterworks network to the manager in bulk and inspecting the waterworks/drainage works is not built yet, therefore the manager should inspect the pipe lines of each waterworks/drain work when malfunction occurs, causing efficiency deterioration and the increase of time and cost.
To solve the above problems, a technology of connecting sensing elements around various kinds of pipes including liquid pipes is suggested on the U.S. Pat. No. 6,265,880, and the above patent details a method of checking whether or not the pipes have defects by using bridge resistance. However, the above US patent has a problem of applying to liquid pipes laid underground, having connection holes after cutting the pipes while laying them underground